This invention relates to an intracompany (or in-company) communication system including a plurality of private branch exchanges (such as Private Automatic Branch Exchanges (PABXs)) and key telephone apparatuses, connected to a LAN (Local Area Network), a WAN (Wide Area Network), or the Internet and, more particularly, to a line selection method and a line selection system for private branch exchanges which are capable of easily establishing private lines. This invention is applicable to any intragroup (or in-group) communication system, without being limited to an intracompany communication system, and is used to establish private lines in exchanges which are connected to a network to construct an exchange system.
In recent years, use is practically made of an intracompany exchange system in which a plurality of private branch exchanges are connected via a network, such as a LAN or a WAN, with VoIP (Voice Over Internet Protocol) introduced therein.
Referring to FIG. 1, a PABX (Private Automatic Branch Exchange) 110A accommodates a plurality of extension terminals 21 and are connected thereto, The PABX 110A is connected through external lines 22 having line numbers 5 and 6 to a LAN 30. Further, the LAN 30 (which serves as the network) is connected to a PABX 110B through external lines 22 having line numbers 1 and 2. Similarly, the LAN 30 is also connected to a PABX 110C through external lines having line numbers 3 and 4. Each of the line numbers 1 through 6 is assigned with an IP address in the LAN 30.
Therefore, if the PABX 110A originates or transmits a call using the line number 5 to the IP address of the line number 1 connected to the PABX 10B, the PABX 110B receives the call with the IP address of the line number 5 as a sender address and the IP address of the line number 1 as a destination address.
With the structure illustrated in the figure, if communications are performed between the two lines of the PABX 110A and the two lines of the PABX 110B, the PABX 110C can not establish external connection to each of the PABX 110A and PABX 110B. It is desired to avoid such a situation and to reserve at least one line available between every pair of the PABXs (between the PABX 110A and the PABX 110B. between the PABX 110B and the PABX 110C, and between the PABX 110A and the PABX 110C). Thus, in case where an intracompany LAN includes a plurality of PABXs, it is necessary to reserve a fixed connection line exclusively for communication between two specific points, such as a private line between the PABXs. However, no prior art disclosing such system is found.
In the intracompany exchange system using the network such as the LAN or the WAN with VoIP introduced therein, specific ones of the private branch exchanges may occupy all the lines in the network so that some of the private branch exchanges can not establish external connection. This is because no private line to fixedly connect every pair of the private branch exchanges is formed.